The invention relates to an internal combustion engine for a motor vehicle and to an exhaust gas turbocharger for an internal combustion engine and to a method for operating an internal combustion engine with an exhaust gas turbocharger.
Due to the continuous tightening of the emission limit values, for example the NO and soot emission values, the demands of exhaust gas turbochargers or charged internal combustion engines also increase. Thus, increasing demands regarding the charge pressure provision with high exhaust gas return rates over average to high load demand regions of the internal combustion engine result, whereby the turbines of exhaust gas turbochargers are increasingly scaled down geometrically. In other words, the required high turbine performances of exhaust gas turbochargers are realized by an increase of the retention ability or by the reduction of the flow capacity of the turbines in cooperation with the respective internal combustion engine. A further influencing of the performance of exhaust gas turbochargers results by exhaust gas aftertreatment systems as for example soot filters, catalysts or SCR systems arranged in the exhaust gas tract downstream of the turbine. These exhaust gas aftertreatment systems lead to a pressure increase at an exhaust gas outlet of the exhaust gas turbocharger. This again effects a reduction of a turbine pressure drop describing the performance of the exhaust gas turbocharger, wherein the turbine pressure drop can be determined as a quotient of a pressure in front of the turbine wheel or an exhaust gas inlet of the turbine housing and a pressure behind the turbine wheel or an exhaust gas outlet of the turbine wheel. Also due to this reason, the turbine size has to be designed again to smaller values and thus lower efficiencies in order to be able to satisfy the performance demand of the compressor. A certain improvement is hereby offered by exhaust gas turbochargers known from the state of the art, whose turbine housings comprise two spiral channels through which exhaust gas can be directed independently to the turbine wheel and that are usually formed in an asymmetric manner, which are respectively coupled to different exhaust gas lines of an exhaust gas tract of the internal combustion engine. The exhaust gas lines on their part are thereby associated with different cylinders or cylinder groups of the internal combustion engine.
Such an internal combustion engine with an exhaust gas turbocharger is for example known from DE 100 48 237 A1. The exhaust gas turbocharger comprises a compressor in an intake tract of the internal combustion engine and a turbine in an exhaust gas tract of the internal combustion engine. The turbine thereby has a turbine housing which comprises spiral channels coupled to an exhaust gas line of the exhaust gas tract and a turbine wheel, which is arranged within a receiving space of the turbine housing and which can be acted on with exhaust gas of the internal combustion engine fed through the spiral channels for driving a compressor wheel of the compressor connected in a rotationally fixed manner to the turbine wheel by means of a shaft. The turbine housing is additionally provided with a variable turbine geometries including for example pivotable guide vanes which are disposed in the nozzle flow cross sections of the spiral channels leading to the space receiving the turbine wheel and which can be adjusted by means of the pivotable guide vanes.
With the design boundary conditions of exhaust gas turbochargers, which are usually defined by the nominal operating point, the charging change side and the usage side of the internal combustion engine, in particular the lower load and speed region of internal combustion engines can however not be served optimally even by exhaust gas turbochargers with two asymmetric spiral channels. The spiral inlet cross section of the spiral channels has to be chosen to be relatively small up to now for this purpose, in order to be able to generate the necessary exhaust gas flow speeds. With the cost-efficient sand casting methods usually used for producing the turbine housing, there are additionally manufacture-technical limits, so that only spiral channels with nozzle cross sections over 4.5 mm can be reasonably accurately produced. Thereby, comparatively high tolerances of 10% and more result with the casting, which leads to efficiency losses of the exhaust gas turbocharger.
It is thus the object of the present invention to achieve an efficiency improvement in larger operating ranges of a charged internal combustion engine with cost-efficient production methods.